This invention relates in general to seals and more particularly to lip seals that have the capability of venting the spaces isolated by them.
Radial lip seals are commonly used in conjunction with antifriction bearings and when other interfaces in the bearing assembly are closed, the seals will isolate the space occupied by the rolling elements and raceways of the bearing so that lubricants will be contained within that space while contaminants will be excluded from it. Indeed, the automotive industry makes extensive use of lip seals in the wheels of both front wheel drive and rear wheel drive automobiles. Many of the seals of current manufacture employ elastohydrodynamic sealing mechanisms, which means that they have special configurations which pump any lubricant that passes under the seals back toward the spaces enclosed by the seals. In the typical seal, these special configurations are triangular, but they may also be sinusoidal or wave-like.
In any event, seals of current construction are perhaps, too effective, at least when operating under elevated pressures within the sealed region. In this regard, the typical radial lip seal, despite its name, has a lip which extends generally axially over a wear surface against which it seals, and contacts that surface along a radially directed extension of the lip (see FIG. 1). An oil film normally exists between the lip and the wear surface. Usually the normal resillency of the elastomer from which the seal lip is formed is sufficient to maintain the seal lip against the wear surface, but in larger seals, such as the type used with railroad bearings, springs are employed to insure that continous contact exists between the seal lip and the wear surface. Should the pressure increase in the space isolated by the seal, that is within the interior of the bearing as could well occur if the bearing operates at elevated temperatures, the increased pressure will exert an inwardly directed force on the axial portion of the seal lip and cause the lip to press even tighter against the wear surface (see FIG. 2). Thus, the space isolated by the seal remains at the elevated pressure.
To overcome this problem, some seals include vents, but small seals of the type used in automobiles often do not have enough unobstructed surface area to accommodate an effective vent. Furthermore, seals with vents incorporated into them must be oriented correctly, usually with the vent presented upwardly, in order to avoid loosing the lubricant through the vent under elevated pressures. Also, some vents remain open continously, and as a consequence the lubricant may leak from them even during normal operating conditions, or contaminants such as dust and water may be drawn in through them.